Rotten Wood Repair Kits for Windows, Doors, Boats – Permanent, Waterproof & Flexible


Rotten Wood Repair Kits are ideal for the restoration of Windows, Doors and Boats, anything made of wood with a rotten area is an ideal candidate for restoration with a repair kit. These are premium repair kits, comprised of a pair of very high performance two part products.

(10 customer reviews)

Rotten Wood Repair Kits are ideal for the restoration of Windows, Doors and Boats. Anything made of wood with a rotted area is an ideal candidate for restoration with a repair kit.

These are premium repair kits, comprised of a pair of very high performance two part products. These kits may appear expensive, but the real cost of any repair is always time and never the materials. That is of course the time required to do the job ‘properly’. These kits can make a permanent waterproof repair. Do it once – do it right.


This is the Make Wood Good American site. From here we can ship pallets worldwide but parcels only surface (UPS), meaning US and Canada, or via freight-consolidators to Hawaii, Puerto Rico and the Caribbean islands.

If you need to ship parcels to Europe, visit one of our European sites by clicking the closest of the two European flags on the header.

How will this rotten wood repair kit repair my rotted wood?

The CPES will consolidate rotten timber. It penetrates deeply into the damaged rotted wood to consolidate and toughen it whilst stopping the rot completely. The Fill-It filler will bond strongly to the CPES saturated timber. This makes a permanent flexible repair which is bonded to the underlying wood. Your rotten wood repair will be permanent – the rot will not return.

CPES seeks out all of the rotting wood not just that which is clearly rotted. CPES also finds the timber that has just started to rot underneath it. CPES will saturate all of this timber, and the rotted timber will rot no more.

There is a lot more you can read about the science of penetrating epoxy sealer in rotten wood repair here.

The performance of these products at repairing rotten wood is evaluated at WoodRestoration.Com. The penetration is pictorially illustrated here at Rotted Wood Repair with CPES.

rotted wood repair six steps to restoration

Why is this better than other Rotten Wood Repair Products

Smiths CPES and Fill-it

This kit contains the worlds finest penetrating epoxy. It penetrates deeply and will find all rotten wood. You do not have to carve out all rot. CPES will find the wood that has started to rot underneath the visible, and penetrate that too. You cannot put filler in on top of timber with rot still in it if you wish to perform rotten wood repair properly.

The filler is also a two part epoxy. Fill-It flexes with the wood so it won’t crack out over time. Boat hulls may be repaired below the waterline with Smiths Fill-It as it is so waterproof. Fill-It is an aggressive adhesive and will bond permanently to the CPES treated timber ensuring a permanent repair.

Colour the filler to match the wood if  a natural or varnished finish is required using our colouring kit.

The filler will bond permanently to stable epoxy saturated wood. Most importantly the repair will last, saving time and money in the future.

The Competition

Competitor wood hardener products are normally an acrylic (Perspex is a well known brand of acrylic) base dissolved in a solvent. This is a simple, one part product which is optimised for convenience rather than performance. It’s performance does not compare to that of Clear Penetrating Epoxy Sealer, and the acrylic does not bond anywhere near as firmly to wood fibres as the wood derived resin in Smiths CPES.

We regularly get customers who have used the popular one part wood hardener products who find the repaired area just pops out as it is sitting on top of active rot still. This is simply not a viable rotten wood repair; if all the rot is not treated – it will return.

Many of the competitors wood fillers use a polyester filler. You can identify Polyester fillers by the relatively small amount of hardener they contain. They are similar in basis to the body fillers used for car repairs. Polyester fillers do not stick as well to wood as epoxy resins, and can have restricted flexibility – leading to failures of your rotten wood repair.

The poor performance of the acrylic wood hardener normally leads to the whole repair plug falling out of the rrotten wood repair first, but this process will be speeded by the relative lack of flexibility of the polyester hardener.

We will be conducting some real world testing of common wood repair products performance against CPES and Fill-It in the near future. Check back to see the results.

Will It Save Money?

The final finish, whether paint or varnish, will bond thoroughly to the CPES reducing maintenance costs and increasing durability. It is often far cheaper to repair rotting wood than replace the rotted wood with new, and these products will affect a permanent repair that will last.

Get a 5% discount by purchasing CPES and Fill-It together as a repair kit.

rotten wood repair kit epoxy resins fill-it cpes

Rotten Wood Repair Kit Instructions:


  • Remove any paint from the rotten wood repair area. Remove paint or varnish from the entire piece if you can.CPES will make any good wood very resistant to rot in the future. Further it will ensure your paint or varnish finish lasts much longer
  • Use your fingers to remove any completely rotted wood. Retain anything firmer than this as CPES will harden rotted wood to the point where it will carry screws and filler without failure
  • Allow the wood to dry out thoroughly before continuing with your rotting wood repair. Dry timber is much easier for the CPES to penetrate into
  • Before applying CPES ensure that you can keep the work area dry until it has released all of the solvents

Application – CPES

  • Apply several coats of CPES to the wood with rot, allowing the wood to absorb as much as it can
  • Use Cold Weather formula for treating rotted wood, as it evaporates faster. You may use Warm Weather formula if you already have some, or need warm formula for another purpose as well. CPES warm formula however will take longer for the solvents to evaporate
  • Apply multiple coats within one day if the solvent smell has dissipated
  • Keep mixed CPES covered between coats
  • Deep areas of rot can have holes drilled into them to assist getting CPES deep into the section of rotted timber
  • Use our CPES injection syringe to apply CPES to areas of deep rot with poor access. It is perfect for saturating rotten timber joints in window frames. The Injection syringe is invaluable for application of CPES to a precise area.  Areas with rotted end grain will absorb a lot of CPES during restoration
  • CPES that dries with a sheen indicates that the rotting or rotten wood is saturated, and will absorb no more
  • Allow 24 hours to dry and partially set after the final coat. There should be no solvent smell and the surface should be firm to the touch. Large sections of rotted timber can take much longer for the solvents to evaporate. This is because they will absorb much more CPES into the rot. Moving air with fans can speed this process

Application – Fill-It filler

  • Take identical quantities of filler from each pot using one tool for each pot. Our glue mixing sticks may assist here
  • Now mix and use the fill-it filler to restore the profile on any rotten areas removed during preparation
  • Force Fill-It onto the substrate using a scraper or palette knife to thoroughly wet the substrate and ensure good adhesion
  • Add filler to restore missing material after wetting the surface
  • Colouring Kits are available if required and may be used to colour the filler to the colour of the damaged wood to allow varnish or clear finishes to be applied
  • Full details on Fill-It, including thorough mixing instructions can be found on the Fill-It Flexible Epoxy Filler


  • Allow the filler to set before any final finishing
  • Finish the Filler by carving or sanding
  • Apply a final sealing coat of CPES over the filler and wood. This will promote the adhesion of your paint or varnish top coat, reducing maintenance and extending life
  • Your rotten wood repair should now be complete, and will just require finishing. The timber should now be very hard and highly resistant to further rot or water damage. The CPES dries as flexible as wood, and is also micro-porous, so the surface is very hard to damage yet will still allow the timber to breathe
  • Apply the first top coat 24 hours after the final coat of CPES typically. The CPES should be dry to the touch, and not smell of solvents, but still be chemically curing. It will bond to the top coat as it cures, gluing it to the wood in a very permanent manner. You may use micro-porous paints over Smiths CPES as the restored wood will still breathe

Each kit includes comprehensive instructions between the two cans of CPES.

If you have specific problems, such as nail rot, we can advise you on how best to deal with those. Please contact us for assistance if this is the case.

Here is a full pictorial walkthrough of repairing a badly rotted wooden window.

What sizes of CPES and Fill-It do I need?

Fill-It Epoxy Filler

1ml of Fill-It fills a void of 1 cubic centimetre. Fill-It Epoxy Filler does not shrink on curing. 1cu inch is 15 cubic centimetres, ml or cc’s. I include imperial measurements as I find it far easier to calculate volumes of cracks etc in inches. Examine your hole after you have removed any loose rotten timber as described above.

Unless you plan to use the entire pack of Fill-It at once you must use two separate tools to remove part A and part B from their containers.

For estimation purposes our packages contain the following amounts:

Package MilliLitres (cc) Cubic Inches
12 US Fl Oz 355 22
2 US Pint 950 58
1 US gallon 3785 231

Clear Penetrating Epoxy Sealer (CPES) Coverage

Coverage for Rotten Wood Repair

CPES use is very hard to accurately estimate when performing rotten wood repair as it is impossible to judge the porosity of rotten timber by eye.

If you are reading this you are very unlikely to be considering new wood coverage however. For rotten wood repairs use cold weather formula as it evaporates faster if you are buying for the job. If you have warm weather by all means use it – though it will take longer for the solvents to migrate.

Seriously decomposed rotted timber, soft to the point where you can push your finger through it, will consume up to 2 times the volume of the timber to harden it fully. However this will harden mush to a rock hard piece of epoxy around some cellulose fibres. Less badly rotted wood will of course consume less.

It’s nearly impossible to estimate accurately how much any piece of well rotted timber may consume without trying the CPES on the actual timber during rotten wood repair, but if you estimate the same volume of CPES as obviously softened rotten timber that is as good a starting point as any.

The most accurate means of estimating the CPES requirements of your rotten wood is to trial it on an area. The aim is to saturate the rotted timber to ensure adequate penetration. If you are unsure how much you may need – buy more and return unused items to us for a refund.

Coverage for priming new timber with CPES

New softwood or ply will consume around 1 litre per 5 sq metres. Hardwood coverage may be up to 10 sq metres / litre.

Older timber, which willhave increased porosity from exposure to the sun and weather, may consume twice as much.

What About The Rest Of My Old Window Frame?

While repairing a rotten section of any exterior wood item, if the entire exposed surface is cleaned back to bare wood (and dried if it is damp) it can be sealed with CPES whilst the repaired area is being restored.

This treatment will seal the exterior surface of the wood permanently against the elements, particularly protecting end grain and vulnerable areas of the item. It makes sense to stop further rot while performing rotten wood repair.


Smiths Clear Penetrating Epoxy Sealer is a fabulous adhesion promoting primer.

Traditional solvent based paints adhere very strongly to it.

Modern Micro-porous paints work very well over CPES as it leaves a breathable finish.

The firm bond between the last coat of CPES and the top coat reduces future maintenance requirements. Two main reasons exist for this:

  1. Smiths CPES bonds the uppermost fibres together in the timber. This provides a stable base for the topcoat that resists the formation of rot under the topcoat.
  2. Clear Penetrating Epoxy Sealer forms chemical bonds with a topcoat applied while the CPES is still curing. The CPES literally glues the topcoat down to the wood with epoxy strength!

Further Information for Our Rotten Timber Repair Kits

If you are unsure of which temperature CPES you require, click here.

For details of the use of CPES as a primer click here, wood hardener (consolidator) and rot restorer, see here.

To see how wood rots, and why the unique resins in Smiths CPES allows permanent rotten timber repairs, click here,

The rot doctor has just concluded some 5 year exposure testing of Smiths CPES, click here to view the Rot Doctors 5 year exposure test.

There is a European version of this product, available here: Rotten wood repair kits in Europe

Additional information

Weight N/A

Cold, Warm


0.95 Litre – 2 US Pint, 1.9 Litre – 2 US Quart, 3.8 Litre – 1 US gallon, 7.6 Litre – 2 US Gallons

Size Filler

12 Oz, 2 Pint, 1 Gallon


Smiths Clear Penetrating Epoxy Sealer (CPES) MSDS

Cold Weather Formula



Warm Weather Formula



Smiths Fill-It MSDS

Fill-It Part A SDS

Fill-It Part B SDS

10 reviews for Rotten Wood Repair Kits for Windows, Doors, Boats – Permanent, Waterproof & Flexible

  1. Chloe Nash (verified owner)

    The product and the customer service were first class. I called to discuss my project and got really friendly and helpful advice and a massive effort to get my order to me on time. Thanks again

  2. paleryder (verified owner)

    Review of Rotten Wood Repair Kit. I came across the products on an American website and followed through to find Make Wood Good and I am very pleased that I did, both Steve and Michelle are a pleasure to deal with and very helpful.
    I am chairman of a group that look after and display an old Pulling & Sailing Lifeboat call RYDER, stationed at Looe from 1902 to 1930 and one of a very few left in the country. She is double diagonal planked on Canadian Rock Elm & Oak. Honduras Mahogany and Rock Elm are no longer available and double diagonal planking can be very expensive to maintain. We are now on our third Rotten Wood Repair kit and whilst it is more expensive than other products it is far superior and has saved us a lot of money by cutting down on the need to have shipyard repairs. The CPES is far easier to apply than similar types of product being of a thinner consistency and the two pack epoxy filler is in my opinion far superior to its competitors and again easier to apply and sand down.
    This is only the second year that we have used these products but we are very impressed so far.
    Tony White
    Chairman Project Ryder.

  3. bennerley1

    I’ve recently purchased this product as i had some windows that had areas of rot . I was so pleased with the results of the cpes that I decided to purchase some more . I have used it as a primer on all the windows after stripping them . The epoxy filler leaves a super smooth finish ready for painting and the two colours make sure you have mixed it thoroughly before using . I now intend using the cpes on a hardwood deck as a primer after stripping before re varnishing

    Natalie Scott

  4. mari2ot

    I have used a small repair kit on an outdoor beam at the bottom of a rather flimsy construction of wooden slats which forms the ‘wall’ of a small conservatory.
    I followed the instructions as far as I could, although I was unable to remove the old paint in some places.
    I am very pleased with the result and the repair has survived the winter very well and no more leakage.
    The Product is exactly what it promised to be and I hope the repair will continue to last a long time.
    I would also like to say that you have been very helpful to me on the phone, thank you.

    Mariann Howell

    • Stephen Dakin (verified owner)

      Many thanks for your kind words Mariann. Good customer service is highly valued by us – hope you get many more years from the repair.

  5. gb (verified owner)

    Extremely good product. Won’t know too much about the clear epoxy for a few years, but hopefully it will do what it says in the tin. The filler itself is good in that the two colours ensure you mix it correctly. (best to use the provided gloves as it is a little sticky)
    Once set (and it needs a reasonable temperature as very cold days means it takes more than 24 hours) it can be carved and sanded. Leaves a super finish for painting.
    First impressions are; this product is really a very, very good one.
    One point is to ensure you calculate the volume you will need as it doesn’t really go too far. It will save you having to reorder all the time,

  6. masterworks (verified owner)

    I have used these products for over 20 years. I know the inventor personally as I had a warehouse next to his in Richmond, CA. I used to go into his shop to purchase and to discuss bonding mechanisms and restoration methods. I know the science behind these products is solid. I know they work. My review is about this company, Make Wood Good. I recently moved to Europe and thought it might be more difficult to get these products. Thank God I found Make Wood Good. I had a problem with the payment method at first, but the owner called me directly and fixed it right away on the phone and sent me the products quickly and professionally. What more do you want? Friendly service the way it should be is exactly what I received. I will purchase exclusively from this company as long as I am in Europe. If you find somebody solid and good… stick with them!!!

  7. Jeremy Hamilton

    Wood filler. This is an excellent product – really helped us restore our ancient, but loved windows. Easy to work with – we would advise however that during a heat wave, you get less workable time than on a cooler cloudy day!

  8. andrew stephene

    so far so good. Only used a small amont so far but results excellent

  9. Michael

    Sealer & Filler. Only time will tell but if using these products on some early rot in my window frames cures the problem then 5 stars would be well deserved. th sealer/hardener was easy to apply & appeared to penetrate well. Unlike other epoxy based products it was slow to cure giving it time to penetrate deeply. The filler was quite easy to mix & apply even to vertical sections. Once again its slow cure allowed time to squeeze it into difficult timber sections. once set it is very hard but capable of being cut & sanded rather like a hardwood. So far I am very impressed & have recommended it to others including a local builder.

  10. Keith Jones

    Amazing Product. I purchased the small repair kit to repair the base of a load bearing strut support a small gable window that had partially rotted. These products are amazing, customer support is second to none, even on a Sunday. Followed they instructions to the letter and the repair is as good as the original. I was pondering whether to purchase because of the cost, but I can assure you this is well worth the money. The only other alternative was to remove the base of the strut and splice in a new piece which would have been difficult and expensive.

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